1. Field of the Invention
The present invention relates generally to the field of tanks, bins and silos for storing materials having fluid properties, and more particularly to an improved bin having a cable-wrapped thin and flexible side wall made of fiberglass reinforced plastic material, which is reinforced to withstand substantial vertical pressures.
2. Description of the Prior Art
Many types of bins and silos suitable for storing granular materials have, of course, been heretofore developed. Most of these have been formed of a suitable metal or concrete because such materials are relatively rigid and have high moduli of elasticity. One example of such known silo construction is shown in U.S. Pat. No. 3,307,311.
However, in recent years, it has become common practice to treat agricultural products with formic acid to kill animal and bacterial life. Unfortunately, formic acid is known to attack both steel and concrete.
In a collateral field, it has been known to form large capacity liquid storage tanks from a thin-walled fiberglass reinforced plastic (FRP) material, reinforced by a cable helically wound around the side wall. While such FRP material is not attacked by formic acid, the use of such tanks has been limited to liquids because such tanks have heretofore not been designed to resist dynamic vertical loads.
The principal problem in adapting such cable-wrapped FRP tanks to store granular materials has been in the area of designing such structures to withstand vertical loads. Unlike a liquid, which does not exert a vertical load on the side wall of a tank, granular materials do exert such vertical loads. The problem is further complicated by the possibility that such granular materials may become undermined during a bottom-unloading operation, the effect of which may be to leave a relatively large mass of suspended material supported only by the side wall.
The side wall of such an FRP tank could be reinforced to support vertical loads by the placement of certain columns about the outside of the tank, but this would interfere with the operation of the side wall-encircling cable.
Various aspects of such cable-wrapped FRP tanks, designed to store liquids, are shown in U.S. Pat. Nos. 3,025,992, 3,917,104, and 3,990,600.